Lecture 12: Blood Transport of Gases/ Regulation of Respiration

Question 1

What is oxygen transport in blood?

Answer 1

-Most of the oxygen in blood (>97%) is reversibly bound to hemoglobin
-Rest circulates dissolved in blood
-Henry’s Law: amount of gas dissolved is directly proportional to partial pressure of that gas however solubility of O2 very low in aqueous solution
-At a usual arterial pressure (PaO2=100mm Hg): 3ml of O2 per L of blood is dissolved ie max physically dissolved if push it will create gas bubbles
-In reality blood leaving the lungs contains ~200 ml O2 per L which results in 197ml/L bound to hemoglobin (packed away in red blood cells)

Question 2

What is the purpose of hemoglobin?

Answer 2

-“solution to take O2 away from solution”-prof
-Contains 4 heme groups, each with 1 iron atom that can bind 1 molecule of O2 (1hemo binds 4 O2 molecules)
-Oxygen saturation is the amount of oxygen carried divided by the total oxygen capacity of blood
-% saturation = amount O2 bound/max capacity of Bh for O2
-When all 4 sites of all the blood Hb are bound: saturation= 100%
-When half the potential binding sites are occupied: saturation = 50%

Question 3

What is the saturation curve?

Answer 3

-Binding of O2 to Hb follows a mass action law
-What drives the curve is at equilibrium: Hb +. O2. <–>. HbO2
O2 diffuse to Picks up O2
tissues heme release more binding
O2
Less binding

-If the concentration of 1 reagent changes, the equilibrium is displaced
-pO2 is responsible for the input of O2 dissolved in blood
-Saturation directly linked to the pO2 (lungs and tissues)
-Blood in lung capillaries=dissolved O2 increase = more HbO2
-Blood passes through tissue capillaries=dissolved O2 decrease = dissociation of HbO2 occurs

Question 4

What shape is the Oxygen saturation curve?

Answer 4

-sigmoid shape
-Relationship b/w Hb content and the pO2
-Under normal conc. (100% sat out of lung, and 75% sat out of tissue)
-Since Hb completely saturated in the lungs main factor is the conc of Hb
-1g Hb caries 1.34ml of O2
-Normal conc.=150g/l –>200ml of O2
-Anemia: O2 transport reduced proportionally to amount of Hb
-In high altitude pO2 in air decreases —> compensated by increasing the number of erythrocytes and Hb )can increase heme and carrying capacity which creates delta P in blood to promote diffusion)

Question 5

What are factors that affect Hb saturation?

Answer 5

1. pH: increases in metabolism= increase in H+
   -Decrease affinity of Hb for O2
   -Curve shifted to the right: need higher pO2 saturation, unloading occurs more rapidly
2. Temperature: increased metabolism=increased heat
   -Result similar to acidity (thing about muscles the energy generated in heat)
3. 2,3DPG (diphospoglycerate): result from glycolysis in erythrocytes, Binds to Hb (has similar effect as the others(

*note the pH, Temp, and DPG mainly affect the unloading (convenient during exercising) therefore higher temp, lower pH and more DPG will make the offloading occur faster for O2

Question 6

What is the blood transport of CO2 and that mechanisms are involved?

Answer 6

Carried in 3 forms:
1. Physical solution (5-10%)=dissolved in blood (20x more soluble in water than O2)

2. Carbamino compounds (bound to proteins)
   -Bind to -NH groups on proteins, especially hemoglobin
   -Stronger affinity for deoxyhemoglobin (no O2) 15-20% of total carbon dioxide content
3. Bicarbonate (HCO3-) 70-75%
   -CO2+H2O<—>H2CO3<–>HCO3- + H+
   -Reaction in erythrocytes
   -HCO3- diffuse in plasma (much more soluble than O2)
   -In the lung opposite reaction occurs (back to CO2 form)

Question 7

What is the regulation of respiration?

Answer 7

-As the heart, respiratory muscles contract rhythmically
-Contrary to the heart, no pace maker cells= skeletal muscle needs AP’s from motor neurones
-Ventilation is automatic and is constantly adjusted to needs
-Rhythmic of the brainstem, (medulla oblongata)

Question 8

What is the respiratory centre?

Answer 8

-Net work of synchronized neurons within the brainstem
-Inspiratory neurons stimulate motor neurons in the spinal cord results in contraction of respiratory muscles
-Inspiratory neurones controlled by another network in the strain stem: Central Pattern Generator (CPG)
-Respiratory centre under constant influence of pO2. pCO2 and H+ conc.
-Inspiratory neurons also under the influence of stretch receptor in the lung, bronchiole and muscles (if get overworked a safety measure to slow things down
-Reflex: Stretch –> sensory fibre–> brain stem–> decrease activity

Question 9

What are chemo receptors and what do they do?

Answer 9

-Chemoreceptors detect )2, CO2, and H+

Central chemoreceptors:
-In brainstem
-Indirectly detect changes in pCO2 in blood to brain
-CO2 enters cerebrospinal fluid by diffusion from the blood across the blood-brain barrier, transformed into HCO3- + H+ –> H+ is the trigger
-Cerebrospinal fluid converts CO2-> CHO3+H+

Peripheral chemoreceptors:
-In carotid and aorta
-Dectect direct arterial changes in pO2, pCO2 and H+

-Info sent to respiratory centres: increase pCO2, increase H+ or decrease pO2 which leads to increase in ventilation (any changes result in increase in vent. in attempt to solve changes)
-pCO2 most important factor that leads to increase in H+ (from brain to periphery)